The Republic of the Marshall Islands (RMI) Maritime Administrator has completed its Marine Casualty Investigation Report into the loss of the very large ore carrier (VLOC) Stellar Daisy - with the ship's classification society Korean Register disagreeing on some key points.
The Stellar Daisy sank in the South Atlantic Ocean on March 31,2017. Two crewmembers were rescued by a vessel in the vicinity and 22 crewmembers are missing and presumed dead.
The Administrator’s investigation determined that the likely direct cause of Stellar Daisy foundering was a rapid list to port following a catastrophic structural failure of the ship’s hull that resulted in a loss of buoyancy and uncontrolled flooding. The structural failure and flooding are thought to have begun in the No. 2 port water ballast tank (WBT) and then progressed rapidly to include structural failure and flooding in multiple WBTs, voids and cargo holds.
The structural damage was likely due to a combination of factors, including the strength of the ship’s structure being compromised over time due to material fatigue, corrosion, unidentified structural defects, multi-port loading and the forces imposed on the hull as a result of the weather conditions the vessel encountered in the days preceding the casualty.
Stellar Daisy was built as a Very Large Crude Carrier (VLCC) in 1993 by Mitsubishi Heavy Industries and was classed with ClassNK. In 2008, Polaris Shipping took responsibility for the ship’s commercial operation and Syncro Shipping took responsibility for the vessel’s management. In the same year, the vessel transferred class from ClassNK to Korean Register (KR). The ship was converted to a VLOC in 2008 at the COSCO Shipyard in China under the supervision of KR.
The investigation concluded that likely causal factors include:
1. the large port and starboard wing tanks increased the potential for a major structural failure and loss of buoyancy in the event that one or more of these tanks flooded while the ship was in a laden condition;
2. a gap in the additional safety measures for bulk carriers contained in SOLAS, Chapter XII, regulation 5 which does not require an assessment to ensure bulk carriers of 150 meters or more in length of double-side skin construction, designed to carry solid bulk cargoes with a density of 1,000 kilograms per cubic meter (kg/m3) and above, constructed on or after July 1, 2006 with any part of the longitudinal bulkhead located within B/5 or 11.5 meters, whichever is less, inboard from the ship’s side at a right angle to the centerline at the assigned summer load line can withstand the flooding of any one wing tank in all loading and ballast conditions; and
3. ineffective assessments of structural damage identified when the ship was in dry dock in 2011, 2012 and 2015 which failed to determine the cause of the structural damage, identify any potential defects with the conversion design or require the development of appropriate repair plans.
Potential contributing factors include:
1. inconsistent compliance by Polaris Shipping with both KR requirements for reporting structural defects and the Administrator’s requirements for reporting marine incidents and marine casualties;
2. ineffective enforcement by KR of the classification society’s rules to ensure Polaris Shipping was reporting identified damage;
3. non-compliance by KR with the requirements in the 2016 RO Agreement to notify the Administrator of, among other things, “any dangerous occurrences, accidents, machinery or structural breakdowns, or failures that they are aware of on a Vessel;” and
4. the less stringent requirements of the 2011 ESP Code regarding the schedule of annual inspections of WBTs on bulk carriers due to deterioration of coatings when compared to those for WBTs on tankers
Korean Register Disagrees with Some Findings
KR has issued a statement saying that it agrees with the majority of the content contained within the report and concurs that the most likely explanation for the loss of the vessel was due to a catastrophic structural failure of the ship’s hull which probably began in No 2 Port WBT. KR agrees with the report (page 62) that the fatigue cracking was probably undetectable by visual inspection prior to the sinking.
In KR’s opinion there are, however, areas of the report that are directed specifically at KR which require further explanation:
KR’s areas of concern are focused on page 71 of the report (Part 3: Analysis):
Material fatigue
The report states: that KR’s review and approval of the conversion design was based on the assumption that all of the scantlings, including those from when the ship was constructed as a VLCC in 1993, were as original and did not take into account material fatigue. The basis for this assumption was that the Finite Element Analysis (FEA), which was conducted in accordance with the requirements of the KR Rules for Steel Ships, took into consideration allowable stress, corrosion, and stresses due to local notch effect.
KR responds: the report correctly states that the FEA and fatigue strength assessment took into consideration allowable stress, corrosion, and stresses due to local notch effect. This is common practice for many IACS classification societies. An independent review conducted by BSR (Bruce S. Rosenblatt & Associates) – the third-party hired by RMI to technically review the conversion process - confirmed that KR’s structural analysis was conducted properly.
Failure analysis
The report states: that although KR did conduct a failure analysis of the damage to the transverse bulkhead at frame No. 65, it did not conduct a failure analysis after an extensive number of cracks were identified and repaired when the ship was in drydock in 2011, within two years after the conversion was completed. As a result, potential weaknesses with design details were not identified. This is an indication that KR’s monitoring and assessment of the ship’s structural integrity was not as effective as it might have been.
KR responds: a failure analysis is carried out at the discretion of the attending surveyor when, in their assessment, a defect or damage is “out of the ordinary” and further scrutiny is required. This is in accordance with KR procedures and in common with other IACS classification societies. The RMI report correctly states that a failure analysis of the damage to the transverse bulkhead at frame No. 65 was conducted as it was determined by the attending surveyor to be “out of the ordinary” and similar damage was not found in other parts of the ship. However, the cracks/defects identified and repaired at the time of drydocking in 2011 were determined to be those typically found on board ships of a similar age (note that Stellar Daisy was 18 years old in 2011). Based on this observation, the attending surveyor determined that the cracks/defects were not “out of the ordinary” and as long as proper repairs were performed, a failure analysis was not needed.
Reporting to flag Administration
The report states: that KR is authorized to serve as an RO on behalf of the Administrator. The 2016 RO Agreement between the Administrator and KR requires that KR immediately inform the Administrator of, among other things, “any dangerous occurrences, accidents, machinery or structural breakdowns, or failures that they are aware of on a Vessel.” KR did not inform the Administrator of the damage to frame No. 65 in 2016.
KR responds: As stated in the casualty investigation report, a failure analysis was carried out to assess the structural integrity of damage to the transverse bulkhead at frame No. 65, the result of which showed that there was no area of concern and proper repairs were undertaken to renew the damaged part to its original condition. KR also examined the surrounding bulkheads of Stellar Daisy as well as bulkheads on 29 other converted VLOCs (approximately 230 bulkheads in total) to determine if there were any similar defects. The result of this extensive investigation was that there were no areas of concern. As a thorough inspection and comprehensive repairs were undertaken, KR determined that there was no “dangerous” structural issue that warranted reporting to the flag Administration.
However, mindful of the recommendations in the report, KR plans to review its reporting procedures to avoid any future misunderstandings.
Source: maritime-executive.com
